This invention relates to a magnetic fluid bearing and more particularly it relates to a magnetic fluid bearing utilizing a magnetic fluid and an electromagnet.
A magnetic bearing supports a rotary shaft by utilizing the attracting or repulsive force of magnetism of either a permanent magnet or an electromagnet so as to control a position of the center of the shaft.
A magnetic fluid is a colloid of fine particles of a ferromagnetic material in solvent. The fluid is automatically magnetized when an external magnetic field is applied to it. In other words, it can be positionally controlled by means of a magnet.
Japanese Patent Laid-open No. 62-202526 discloses a magnetic bearing utilizing a permanent magnet and a magnetic fluid.
With such an arrangement, a hollow disc-shaped magnet is fitted to a shaft made of a magnetic material and the radial gap between the magnet and the shaft is filled with the magnetic fluid to form a magnetic circuit. By a concentration of the magnetic flux of the magnetic fluid, a liquid 0-ring is formed by the magnetic fluid to seal the gap.
Since a magnetic fluid is used as sealing means and a permanent magnet is used as a magnet, it is necessary to prepare a permanent magnet having a magnetic effect that can meet the load condition of the bearing and formation of a sleeve by using it for each application of a bearing of this type.
Moreover, the manufacturer of such a known magnetic fluid bearing is required to fabricate and store a wide variety of permanent magnets in large quantity to meet the above requirements, entailing a large and complicated manufacturing line and an enhanced cost for management of such a manufacturing line and a large inventory.